Cruise operations were conducted on the continental shelf
(depths to 350 m) in the Gulf of Maine and northern Georges Bank regions,
including the Canadian Exclusive Economic Zone on eastern Georges Bank. The
2011Fall Atlantic Herring Acoustic Survey was conducted during three parts
between 7 September and 14 October 2011 (Figures 1-3). Part 1 of the survey
(7-16 September) was dedicated to calibrating the scientific echo sounders on
the FSV Delaware II, collecting acoustic and optical data with the
Advanced Fisheries Tow Vehicle (AFTV), and conducting a collaborative
experiment on Atlantic herring in the Georges Bank region. The annual
systematic acoustic and biological survey of Atlantic herring was conducted
in the Georges Bank region during Part 2 (19-30 September) and into Part 3.
Part 3 of the cruise (3-14 October) was dedicated to completing the herring
survey, a fine-scale acoustic survey and experimental acoustic and optical
measurements in the Georges Bank region as well as a systematic survey of
Atlantic herring in the Jeffrey's Ledge, Platts Bank, Fippennies and Cashes
Ledge areas. A net comparison test was also conducted during Part 3 of the
cruise. This study compared the fishing efficiency of the older Irish Herring
Midwater Trawl (IHMT) to the newer Polytron Midwater Trawl (PMRT).

Calibrations are required during each survey to ensure data
quality and verify echo sounder performance. The EK60 was calibrated by
suspending standard calibration spheres of known target strength under each
transducer from three monofilament lines. A calibration sphere was centered
in the far field of each transducer and moved throughout the acoustic beam
beneath the vessel using remotely controlled downriggers. The 18-, 38-, and
120-kHz split-beam transducers were calibrated in Cape Cod Bay. Noise tests
of the EK60 were conducted dockside and while the vessel was underway at 10
knots (survey speed).

Simrad EK60 Scientific Sounder:

The Simrad EK60 Scientific Sounder was the primary sampling
gear used during the acoustic surveys for providing species-specific
abundance estimates. The EK60 operated three hull-mounted transducers (18-,
38-, and 120-kHz split-beam transducers). The EK60 was interfaced via TCP/IP
Ethernet to the FSV Delaware’s SCS server for data logging. RS232
connections were used for navigational (Differential GPS) input. The SCS
Event Log was used to record all operational events (e.g., begin and end
points of transects, stations, gear deployments, and other events that affect
the track cruise and vessel speed) during the cruise.

Advanced Fisheries Towed Vehicle (AFTV):

The AFTV is designed to deploy integrated acoustical, optical,
and environmental sensors for verifying acoustic backscatter from the water
column and seafloor. The AFTV is deployed using a portable fiber optic winch
system equipped with 2000 m of 0.322 cable, and has an overall weight of
about 5,000 lb. The cable has three single mode fiber optic and three copper
conductors, and has an 11,000 lb/ft breaking strength rating. The AFTV
towbody weighs about 900 lb and is approximately 7 ft in length. The AFTV
also has a 100 lb counter weight arranged about 20 m in front of the towbody
to dampen the vessel motion for maintaining the horizontal stability of the
towbody. This requires a two point deployment approach using the vessel’s
A-frame and articulating crane on the aft deck. The AFTV is configured with
an EK60 38 kHz, CTD, motion sensor, DIDSON sonar, and various underwater
cameras and lighting. The AFTV was towed intermittently at relatively slow
speeds (1-3 knots) above the seafloor and throughout the water column to
collect in situ target strength data and verify acoustic
backscatter.

Dual-frequency IDentification SONar (DIDSON):

A DIDSON sonar was installed on the AFTV throughout all three
legs of the cruise. The DIDSON uses acoustic lens technology to collect very
high resolution acoustic data. Using the DIDSON, individual fish and their
behavior can be monitored out to approximately 20 meters from the towbody.
The DIDSON was located in the forward portion of the AFTV and was mounted on
a Sidus pan and tilt assembly to allow for a variety of viewing angles.

Acoustic Survey Operations:

EK60 data were collected continuously throughout the cruise.
During the surveys, a constant ship speed of 10±1 knots was maintained.
Vessel speed was reduced to no less than 8 knots during rough seas. EK60
operations were generally suspended when seas exceeded 2 m. Each transect was
assigned a sequential number throughout the cruise. A transect was defined as
a portion of the cruise track with a constant heading and ship speed. All
scientific gear deployments were also assigned a unique, sequential
deployment number.

EK60 Target Strength Measurements:

Target strength measurements with the hull- mounted EK60
split-beam transducers and with the AFTV-mounted 38-kHz EK60 split- beam
transducer (ES38-DD) were collected on selected fish aggregations. The vessel
was positioned over aggregations, and the towbody was deployed from the
vessel’s aft A-frame. The AFTV would then be towed behind the vessel for
between 1 to 2 hours at about 2 knots while collecting video and acoustic
data.

Myriax Echoview Post-processor:

Echoview (Myriax Ltd.) software v. 4.7. was used for data
acquisition and post-processing of EK60 data during the cruise. Echoview was
used to conduct preliminary post-processing of EK60 data at sea, which
involved removing extraneous bottom echoes and/or water column noise.
Echoview was also used to partition acoustic backscatter to Atlantic herring.
EK60 data and Echoview files were logged and archived directly to the SCS
system via a TCP/IP Ethernet connection. Three computers were set up for the
acoustic data. One computer was used for EK60 data acquisition. This computer
was located in the SCS room and was part of the SCS system. The other two
computers were set up in the dry lab, with one computer used for post-
processing and the other used for viewing data in real time.

Polytron Midwater Trawl (PMRT):

The PMRT midwater trawl was recently purchased to replace the
older Irish Herring Midwater Trawl (IHMT) that has been in use on previous
surveys. The PMRT is a hybrid design, and incorporates features from both the
High Speed Midwater Trawl (HSMRT) and the Irish Herring Midwater Trawl (IHMT)
that have been in use for the past 10 to 12 years. The PMRT was designed to
be fished at speeds of about 4 knots. The PMRT was deployed during survey
operations, and targeted on acoustic backscatter. The PMRT was towed at about
4 knots, depending on trawl performance and water currents. The duration and
depth of the trawls were not standardized, and the Chief Scientist or Watch
Chief communicated with the bridge officers as to the haul duration and
depths. The Simrad FS70 trawl sonar was deployed with every trawl. Officers
recorded the time, date, navigational, and station data in the ship’s
Scientific Computer System (SCS) for each trawl. This data was then pulled
into the Fisheries Scientific Computer System (FSCS). The scientists recorded
the catch and ITI data for each station deployment using the FSCS on-board
entry system. The PMRT was the primary biological sampling tool used during
the three legs of the Herring survey.

Irish Herring Midwater Trawl (IHMT):

The IMHT midwater trawl was used as a backup net to collect
biological samples and verify species composition of acoustic backscatter for
the first two legs, and then as the primary net for the 3rd leg. The IMHT was designed to be fished at speeds of about 4
knots. The IMHT was deployed during survey operations, and targeted on
acoustic backscatter. The IMHT was towed at about 4 knots, depending on trawl
performance and water currents. The duration and depth of the trawls were not
standardized, and the Chief Scientist or Watch Chief communicated with the
bridge officers as to the haul duration and depths. The Simrad FS70 was
deployed with every haul. Officers recorded the time, date, navigational, and
station data in FSCS, while the scientists recorded the catch and ITI data
for each station deployment. Catch data was recorded using the FSCS on-board
entry system.

Simrad FS70 Trawl Monitoring and Third-wire Winch
System:

The trawl was monitored during fishing operations using the
FS70 trawl sonar. The Simrad FS70 Trawl Monitoring System was newly installed
on the FSV Delaware II for this survey. The FS70 third wire trawl
sonar replaced the older FS903 trawl monitoring system. The FS70 is a
third-wire device that provides real-time trawl performance information
through its sonar images of the trawl opening. The scientific party recorded
FS70 measurements on hardcopy forms at specified intervals during each
deployment. The FS70 data was also recorded to the system’s computer hard
drive for archiving purposes.

Scientific Computer System (SCS) and Fisheries Scientific
Computer System (FSCS):

The SCS system is a PC-based server, which continuously
collects and distributes scientific data from various navigational,
oceanographic, meteorological, and sampling sensors throughout the cruise.
The SCS Event Log program was configured for NEFSC Fisheries Acoustic Survey
operations, and was used by the scientists to document all operational events
(e.g., begin and end of transects and deployments). Dates and times
were synchronized using the vessel’s GPS master clock and Dimension IV
software. The FSCS system was used for on-board data logging of the
biological and catch data.

Conductivity-Temperature-Depth (CTD) Profiler:

A Seabird CTD profiler was deployed at the beginning and ending
of each transect, and at the beginning of each scientific gear deployment to
define the hydrographic conditions in the study area. Water bottle casts were
also deployed twice per day to collect salinity samples.

Vemco Minilog Probes:

Temperature-depth probes (set at a 2 sec sampling rate) were
attached to the midwater trawl headrope and footrope during trawl hauls.

Biological Sampling:

Trawl catches were sorted by species, weighed and measured (to
the nearest cm FL) according to standard NEFSC procedures. For Atlantic
herring, subsamples were taken for each trawl haul for detailed lengths (FL
in mm), individual weights (to nearest 0.1 g), sex/maturity staging, and
otolith samples (freeze herring whole). Subsampling protocol was 1 fish per
centimeter length class for herring less than 25 cm and 3 fish per centimeter
length class for herring 25 cm and longer. The FSCS system was used for
on-board entry and auditing of trawl station and biological data. Biological
data were transferred to the NEFSC for auditing.

RESULTS

Part 1

Part 1 was dedicated to calibrating the hull-mounted EK60
transducers, collecting data with the Advanced Fisheries Tow Vehicle (AFTV),
and conducting a collaborative experiment with scientists from the Woods Hole
Oceanographic Institution (WHOI) and the Naval Research Laboratory (NRL). The
AFTV was loaded on the Delaware II, and initial testing, trouble
shooting, and evaluation was completed on the 8th of
September. The Delaware II departed the Fisheries dock on Sept.
8th, and headed to Cape Cod Bay to calibrate the
EK60. A test deployment of the AFTV was conducted on 8 September to educate
new deck crew members on the intricacies of deploying and retrieving the
AFTV. The 18-, 38-, and 120-kHz EK60 echo sounders were successfully
calibrated in Cape Cod Bay on 8 September. Sv and TS
gain setting changes were within tolerance levels (± .25 dB). A CTD profile
was collected at the calibration site. The calibration site was located about
five miles southwest of Provincetown, MA. After the calibrations were
completed, the vessel steamed to Jeffreys Ledge to begin a systematic survey
of herring in this area. Numerous trawls, CTDs, and AFTV deployments were
conducted in this area. On 11 September, the Delaware II proceeded to
the Franklin Swell area to begin the experiment on Atlantic Herring with WHOI
scientists. We conducted joint operations with the R/V Oceanus on the
northern edge of Franklin Swell (Fig. 1). The WHOI scientists were using a
broadband echo sounder and the NRL were using a long-range (out to
approximately 10 km radius) sonar system. The FSV Delaware II
collected EK60 data and biological data. At the conclusion of the experiment,
the FSV Delaware II steamed back to Woods Hole and arrived the morning
of Sept. 16.

During this portion of the cruise 104 deployments (6 AFTV, 65
CTD profiles, and 32 trawl deployments) and 51 transects were completed.

Part 2

The goal of Part 2 was to conduct the annual systematic
acoustic survey of Atlantic herring along the northern edge of Georges Bank
and southern Gulf of Maine. Survey operations included EK60 acoustic data
acquisition, midwater trawl hauls, CTD profiles, and AFTV deployments. The
vessel departed Woods Hole on Sept. 20 and steamed to the northeast peak of
Georges Bank. The vessel arrived on station on Sept. 21 and commenced the
survey (Fig. 2). The survey consisted of parallel transects oriented
north-south with 8 nmi spacing between transects. Survey speed was
consistently 10±1 knots. CTD profiles were completed at the beginning and end
of each transect and immediately prior to or immediately after each trawl
haul. Trawl location were selected on an ad hoc basis to sample the
acoustic backscatter.

This portion of the survey was completed on Sept. 30, with a
total of 37 trawls, 67 CTD profiles, 3 AFTV deployments, and 37 transects
(parallel and crossover) completed.

Part 3

The first portion of Part 3 was dedicated to completing the
herring survey (Fig. 3). The Delaware II departed Woods Hole on
October 4th and steamed to Georges Bank to resume
transects that were not completed during Leg 2 of the survey. All Leg 2
transects were completed on October 7th. The second
portion of Part 3 was dedicated to conducting a net comparison study between
the newer Polytron Midwater Trawl (PMRT) and the Irish Midwater Trawl (IHMT).
Testing commenced on the morning of October 7th. A
total of six trawls (three during the day and three at night) were conducted
using the PMRT net. Once the six trawls were completed, the Delaware
II deck crew removed the PMRT net, and installed the older IHMT net.
Again, six trawls were performed using the IHMT net (three trawls during the
day and three trawls at night). The net comparison study was completed on
October 9th. The Irish Midwater Trawl (IHMT) remained
on the net drum for the remainder of the cruise and was used on all
subsequent trawls. The remainder of Part 3 of the Herring Acoustic Survey was
dedicated to systematic parallel transects along the Fippennies and Cashes
Ledges as well as parallel transects along Jeffrey's Ledge.

Part 3 was completed on October 14th,
with a total of 26 IHMT trawls, 15 PMRT trawls, 62 CTD profiles, 4 AFTV
deployments, and 20 transects.

DISPOSITION OF DATA

Data and results were archived at the Northeast Fisheries
Science Center (NEFSC). Data and results are available on CD-ROM or other
media. Cruise reports and results are also available at the NEFSC
website: